1. Field of the Invention
The invention relates to a semiconductor circuit configuration having a driver circuit which is integrated in a semiconductor substrate of a first conductivity type and contains PV switching transistors for switching positive and zero-value voltage levels. The circuit configuration further has NV switching transistors for switching negative and zero-value voltage levels, and an actuation circuit which is positioned upstream of the driver circuit and is likewise formed in the semiconductor substrate with the semiconductor substrate being connected to a substrate level. The invention furthermore relates to a semiconductor circuit having an inversion and level-changing circuit.
Semiconductor circuit configurations and circuits of this generic type are used in particular as word line decoders for electrically erasable read only memories. The already known word line decoders can only apply two voltages to a downstream cell array at the same time, for example in the case of EEPROMs, the decoder switches between zero and +2.5 volts, for example, during reading or between zero volts and the programming voltage (for example xe2x88x9212 volts) during programming. In certain circumstances, it may be desirable to use a word line decoder to simultaneously apply either a zero level for lines which have not been selected, a positive voltage (for example the supply voltage) and a negative voltage to different signal lines (word lines) at the same time, for selective complementary line pairs. One example of this is the actuation of the word lines in a cell array having ferroelectric cells.
Published, European Patent Application EP 0 522 579 A1 discloses a driver circuit for EEPROM memories, in which xe2x80x9cfloating gatexe2x80x9d transistors are used. In which all source and drain connections of all the transistors in an entire column of the memory array are switched on at the same time by a xe2x80x9csource-columnxe2x80x9d decoder. The driver circuit formed in the line selection circuit is used for simultaneous selection of all the transistors in one line of the memory cell array. In this case, the transistor that switches negative voltages is formed in an additional well.
It is accordingly an object of the invention to provide a semiconductor circuit configuration that overcomes the above-mentioned disadvantages of the prior art devices of this general type, which can simultaneously produce a zero level, a positive voltage and a negative voltage.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor circuit configuration. The circuit configuration includes a semiconductor substrate of a first conductivity type, a first line, a second line, a first individual line, a second individual line, and a substrate level connected to the semiconductor substrate. A driver circuit is integrated in the semiconductor substrate and contains a first and a second positive voltage (PV) switching transistor for switching positive and zero-value voltage levels, and a first and a second negative voltage (NV) switching transistor for switching negative and the zero-value voltage levels. The first PV switching transistor is connected between the first line and the first individual line. The first NV switching transistor is connected between the substrate level and the first individual line, the second NV switching transistor is connected between the second line and the second individual line. The second PV switching transistor is connected between the substrate level and the second individual line. The driver circuit has a number of circuit stages including a stage having an inversion and level-changing circuit. The driver circuit has outputs formed by at least one activation line pair formed of two complementary lines being the first individual line and the second individual line. The first PV switching transistor and the first NV switching transistor are able to connect a first activation voltage present on the first line to the first individual line. The second PV switching transistor and the second NV switching transistor at a same time are able to connect a second activation voltage present on the second line to the second individual line. The first activation voltage and the second activation voltage can be of opposite polarity. The first PV switching transistor and the first NV switching transistor are able to connect the first individual line to the substrate level. The second PV switching transistor and the second NV switching transistor at a same time are able to connect the second individual line to the substrate level. An outer well is disposed in the semiconductor substrate and is formed of a second conductivity type being opposite to the first conductivity type. The first NV switching transistor and the second NV switching transistor of the driver circuit are formed within the outer well, and the is outer well connected to a supply voltage. An actuation circuit is disposed upstream of and connected to the driver circuit and formed in the semiconductor substrate.
The invention provides for the driver circuit to contain a number of circuit stages and for the first stage of the driver circuit to have a first inversion and level-changing circuit. The NV switching transistor of the driver circuit is formed within the outer well, which is embedded in the semiconductor substrate, of a second conductivity type, which is the opposite to the first conductivity type, and the outer well is connected to a supply voltage.
When using conventional CMOS technology, parasitic diodes occur when switching negative voltages in the NMOS transistors, and these result in leakage currents. The invention thus proposes that the driver which follows the actuation circuit, or at least circuit groups or transistors of such a driver, be moved into the outer well. The well is in this case of the opposite conductivity type of the substrate, and is connected to the supply voltage. The advantage of the semiconductor circuit configuration is that the parasitic diodes of the NMOS transistors that are embedded in the outer well can now no longer conduct. The negative voltage which is applied to the well of the NMOS transistors and is to be switched can, in consequence, no longer have any disadvantageous effect on the rest of the circuit that is located on the substrate.
In one particularly preferred embodiment of the invention, the actuation circuit is formed by a decoder having a number of outputs coupled to the driver circuit. It is also advantageous for that output of the decoder which is switched to be active to supply a zero level, and all the other outputs, which are switched to be passive, each to supply a positive potential level in this case.
According to the invention, the outputs of the driver circuit are formed by at least one activation line pair. The activation line pairs, which are formed from complementary individual lines, then carry a zero level on both lines or, in the active state, positive and negative activation voltages, which are connected to the activation line pairs by activation switches following the first inversion and level-changing circuit. The invention also allows a number of activation line pairs to be connected to the positive and negative activation voltages at the same time. In this case, the polarity of potentials on the complementary lines can be interchanged by a selection circuit, which is upstream of the activation switches and defines the activation voltages to be switched through.
The potential of the positive activation voltage can also advantageously be greater than the potential of the supply voltage. In consequence, it is advantageous for the first inversion and level-changing circuit and the activation switches which connect the positive and negative activation voltage to the activation line pairs each to have a protection transistor of a predefined conductivity (NMOS) connected in between. A control connection of the transistor is connected to the supply voltage, a first an electrode connection is connected to the first inversion and level-changing circuit, and a second electrode connection is connected to the control connections of the activation switches.
In a further advantageous embodiment of the invention, the first inversion and level-changing circuit is followed by a second inversion and level-changing circuit, which is connected to the control connections of two deactivation switches, which connect the activation lines to the substrate level. In this case as well, it is possible to switch a number of pairs of complementary lines at the same time.
Protection transistors of a predefined conductivity type are provided. A first protection transistor has a control terminal connected to the supply voltage and electrode terminals connected to the first inversion and level-changing circuit and to the first PV switching transistor. A second protection transistor has a control terminal connected to the supply voltage and electrode terminals connected to the first inversion and level-changing circuit and to the second NV switching transistor.
In one preferred embodiment of the invention, it is possible for the first inversion and level-changing circuit to have an associated holding transistor, for example by a MOS transistor of the positive conductivity type. A control input of the holding transistor is connected to the output of the first inversion and level-changing circuit and whose electrode connections are connected first to the supply voltage and second to the input of the inversion and level-changing circuit. The advantage of the holding transistor is that it supports the high level of the input, thus allowing a standard 1-of-2Nxe2x80x94NAND decoder to be used.
In accordance with an added feature of the invention, the inversion and level-changing circuit, the further inversion and level, the protection transistors, the first PV switching transistor, the second PV switching transistor, the first NV switching transistor, the second NV switching transistor and the holding transistor are embedded within the outer well in the semiconductor substrate.
A further refinement of the invention provides for at least one of the inversion and level-changing circuit configurations to be provided with two transistors of opposite polarity. The transistors are integrated in the semiconductor substrate of the first conductivity type, with at least the transistor of the negative type being formed within the outer well. The outer well is embedded in the semiconductor substrate, with a conductivity type which is the opposite of the conductivity type of the first semiconductor substrate, and with the outer well being connected to the supply voltage. The circuit furthermore has a signal input, which is connected to the control inputs of the transistors of opposite polarity, and a signal output that is connected to a respective electrode connection of the transistors. The two remaining electrode connections of the transistors of opposite polarity are connected first, in the case of the positive type, to the positive supply voltage and, in the case of the negative type, to a negative voltage.
It is furthermore advantageous for at least one of the inversion and level-changing circuit configurations which are formed in a semiconductor substrate to have a signal input which is connected to the control input of a first transistor of the negative type. One of whose electrodes is connected to the negative supply voltage, while its other electrode is connected to the signal output of the circuit configuration. Furthermore, one electrode of a transistor of the positive type is connected to the signal output, while its other electrode is connected to the positive supply voltage and its control input is connected to the signal input of the circuit configuration. Furthermore, an electrode of a further transistor of the negative type is connected to the signal input, while its other electrode is connected to the negative supply voltage and its control input is connected to the signal output. In this case, the transistors of the negative type are formed within the outer well, which is embedded in the semiconductor substrate, of a second conductivity type which is of the opposite type to the semiconductor substrate. The outer well is expediently connected to a supply voltage.
Based on the principle of the invention, a transistor of the positive type is connected upstream of the signal input of the inversion and level-changing circuit. A control input of the transistor is connected to a zero potential, while its electrode connections are connected first to the input signal and second to the signal input of the inversion and level-changing circuit.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor circuit configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.